The market for displays and other devices (e.g., keyboards) having touch functionality is rapidly growing. As a result, touch-sensing techniques using touch screens have been developed to enable displays and other devices to have touch functionality. Touch-sensing functionality is gaining wider use in mobile device applications, such as smart phones, e-book readers, laptop computers and tablet computers.
Touch-screen devices have been developed that rely on the amount of touching force or pressure (force/area) applied to one or more touch locations on the cover sheet. An accurate determination of the touching forces associated with one or more touches is needed for the touch-screen device to respond properly.
The conventional fabrication of a touch-screen device includes securing the cover sheet to a support frame. This is typically accomplished with an adhesive material, such as pressure-sensitive tape, which has substantial pliability or compliance (i.e., a relatively low Young's modulus). Thus, when a touching force is applied, the adhesive material is compressed, and when the touching force is terminated, the adhesive material relatively slowly expands back to its original size.
For most touch-screen devices, the degree of compliance of the adhesive material does not substantially impact the operation of the device. On the other hand, for those touch-screen devices that rely on the force or pressure measurement associated with a touch event, the compression and expansion of the adhesive material can cause an improper measurement. In particular, some portion of the touching force can go into compressing the adhesive material rather than into deforming or displacing the cover sheet, thereby leading to an erroneous force or pressure measurement.